This invention relates to monitor systems that monitor a condition in the vicinity of a telephone circuit and indicate the state of the monitored condition when the phone circuit is called. An existing device of this type shorts out and disables the telephone circuit if the monitored condition is abnormal, and this interferes objectionably and illegally with the telephone circuit.
The invention recognizes the need for a better monitoring system that does not interfere with the telephone circuit and yet indicates the state of a monitored condition when the telephone circuit is called. The invention also recognizes a simple and effective way of accomplishing this with a device that is highly reliable, does not require a power source, is simple to install, does not interfere with the telephone circuit, and can respond in several ways to convey information about monitored conditions when the phone circuit is called. It also does not require answering the telephone circuit or sending messages over the telephone circuit; and it accomplishes its objectives economically, conveniently, and reliably.